This invention relates to a means for variable valve timing for engines and more particularly to an improved valve driving arrangement for an internal combustion engine.
A wide variety of systems have been proposed for varying the valve timing of an internal combustion engine so as to improve its performance. Variable valve timing engines can have the overlap between the intake and exhaust valve vents altered to suit varying running conditions and provide optimum performance over a wide variety of running conditions. For this reason, there is a considerable interest in such variable valve timing mechanisms.
However, one reason why variable valve timing has not enjoyed wider application is its complexity. This problem is particularly acute in connection with engines having banks of cylinders such as V type or opposed engines. Where such engines employ camshafts for the cylinder heads of each bank, it is necessary to insure that the valve timing of the camshafts of the various cylinder heads be adjusted simultaneously so that there is not an abnormal or uneven running condition for the cylinders of the various banks. Because of the previously proposed variable valve timing mechanisms, the application of this principle to V type engines has been severely limited.
It is, therefore, a principal object of this invention to provide an improved variable valve timing device for an internal combustion engine.
It is a further object of this invention to provide an improved and simplified arrangement for achieving variable valve timing for an engine having angularly disposed cylinder banks in a simple and yet effective manner.
It is a further object of this invention to provide a variable valve timing arrangement for an engine having angularly disposed cylinder banks and wherein all camshafts may be adjusted simultaneously by means of a single actuator.
In additional to the aforenoted difficulties in connection with the driving of the camshafts of an engine having angularly disposed cylinder banks and achieving variable valve timing, the drive of the camshafts of the engine per se present several problems. For example, it is desirable to minimize the number of flexible transmitters (either chains or driving belts) that are employed for driving the various camshafts of such engines. By employing only a single flexible transmitter for driving all camshafts, the likelihood of the camshafts becoming out of time with each other is substantially reduced.
There are difficulties that are presented in connection with driving the camshafts of the cylinder banks from each other, however. That is, a portion of the flexible transmitter extends from the camshaft of one cylinder bank to the camshaft of another cylinder bank so as to transfer the drive between the camshafts of the cylinder banks. Normally this is done by including an idler sprocket that is positioned in the bank of the V so as to drive the camshafts of the cylinder banks from each other. However, the use of such an idler sprocket adds considerably to the length of the flexible transmitter and it is desirable to maintain the transmitter length as short as possible so as to avoid the disadvantages encountered when the flexible transmitter stretches, which is natural in operation. The previous type of drives for camshafts employed have, however, not permitted a direct straight flight of the flexible transmitter to exist between the camshaft of one cylinder bank and a camshaft of the other cylinder bank for transmitting the drive between them. The reason for this is that the previous type of drive arrangements have been that such a direct flight between the camshafts of the cylinder banks would substantially minimize the amount of contact between the flexible transmitter and the camshafts. It is desirable to insure that there is a substantial circumferential area of contact between the transmitter and the camshaft sprocket or pulley so as to insure that the drive will not jump out of time.
It is, therefore, a still further object of this invention to provide an improved, simplified and yet effective arrangement for driving the camshafts of engines having cylinder banks disposed at an angle to each other by means of a single flexible transmitter.